Cree XLamp MT-G2 LED 3-Inch Downlight Reference Design

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ApplicAtion note 12 6 r ev 0 C

Cree ^® XLamp ^® MT-G2 LED

3-Inch Downlight Reference Design

InTRoDuCTIon

This application note details the design of a 3-inch downlight that uses Cree’s XLamp

^®

MT‑G2 LED, a multi‑die, high‑flux array optimized for high lumen output directional applications such as downlights, recessed fixtures and can lights. The MT‑G2 offers exceptional lumen levels and efficacy and delivers the industry’s best color consistency and superior optical control.

Three‑inch downlights are commonly used indoors and outdoors in both residential and commercial applications such as soffits and ceilings. The flexibility, high performance and ease of use offered by the XLamp MT‑G2 LED makes it a strong candidate for use in a 3‑inch downlight.

The first EasyWhite

^®

LED array built on the SC³ Technology

^®

Platform, Cree’s XLamp MT-G2 LeD pushes performance limits to redefine lumen levels and efficacy while delivering the industry’s best color consistency and superior optical control. MT‑G2 LEDs are designed for high‑output, directional lighting applications and are the ideal replacement for lighting TabLE of ConTEnTs

Introduction ... 1

Design approach/objectives ... 2

The 6‑step methodology ... 2

1. Define lighting requirements... 2

2. Define design goals ... 5

3. Estimate efficiencies of the optical, thermal & electrical systems ... 5

4. Calculate the number of LEDs ... 6

5. Consider all design possibilities ... 7

6. Complete the final steps: implementation and analysis ... 7

Conclusion ...10

Bill of materials ...10

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Copyright © 2013-2016 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree^®, Lamp^®, EasyWhite^® and SC³ Technology^® are registered trademarks and the Cree logo is a trademark of Cree, Inc. ENERGY STAR^® is a registered trademark of the U.S. Environmental Protection Agency. Other trademarks, product, and company names are the property of their respective owners and do not imply specific product and/or vendor endorsement, sponsorship or association. For product specifications, please see the data sheets available at www.cree.com. For warranty

information, please contact Cree Sales at [email protected].

2 optical control are necessary. The MT‑G2 LED occupies the same footprint and operates with the same drive conditions as the original MT‑G LED, which facilitates a drop‑in replacement.

DEsIGn appRoaCh/objECTIvEs

In the “LeD Luminaire Design Guide” Cree advocates a 6‑step framework for creating LED luminaires. All Cree reference designs use this framework, and the design guide’s summary table is reproduced below in Table 1.

Table 1: Cree 6-step framework

step Explanation

1. Define lighting requirements • The design goals can be based either on an existing fixture or on the application’s lighting requirements.

2. Define design goals • Specify design goals, which will be based on the application’s lighting requirements.

• Specify any other goals that will influence the design, such as special optical or environmental requirements.

3. Estimate efficiencies of the optical, thermal &

electrical systems • Design goals will place constraints on the optical, thermal and electrical systems.

• Good estimations of efficiencies of each system can be made based on these constraints.

• The combination of lighting goals and system efficiencies will drive the number of LEDs needed in the luminaire.

4. Calculate the number of LEDs needed • Based on the design goals and estimated losses, the designer can calculate the number of LEDs to meet the design goals.

5. Consider all design possibilities and choose the

best • With any design, there are many ways to achieve the goals.

• LED lighting is a new field; assumptions that work for conventional lighting sources may not apply.

6. Complete final steps • Complete circuit board layout.

• Test design choices by building a prototype luminaire.

• Make sure the design achieves all the design goals.

• Use the prototype to further refine the luminaire design.

• Record observations and ideas for improvement.

ThE 6-sTEp METhoDoLoGy

The goal of the design is to show the ease of design and implementation of a 3-inch downlight that offers superior performance using one Cree XLamp MT‑G2 LED.

1. DEfInE LIGhTInG REquIREMEnTs

Table 2 shows a ranked list of desirable characteristics for a 3‑inch downlight.

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Table 2: some ranked design criteria for an LED downlight

Importance Characteristics units

Critical

Luminous flux (steady‑state) lumens (lm)

Efficacy lumens per watt (lm/W)

Luminous distribution Color uniformity Form factor

Important

Price $

Lifetime hours

Operating temperatures degrees (°C)

Operating humidity % relative humidity

Correlated color temperature (CCT) K

Color rendering index (CRI) 100-point scale

Manufacturability ease of installation

Table 3 and Table 4 summarize the ENERGY STAR

^®

requirements for luminaires.

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Table 3: ENERGY STAR luminous efficacy, light output and zonal lumen density requirements

Luminaire Type Luminaire Efficacy (Initial)

EnERGy sTaR REquIREMEnTs Luminaire Minimum Light

Output (Initial) Luminaire Zonal Lumen

Density Requirement Downlights:

• recessed

• surface

• pendant

• SSL downlight retrofits

42 lm/W ≤ 4.5” aperture: 345 lumens

> 4.5” aperture: 575 lumens

Luminaire shall deliver a minimum of 75% of total initial lumens within the 0‑60° zone (axially symmetric about the nadir)

Table 4: ENERGY STAR luminaire requirements

Characteristic Requirements

Light source life requirements: all

luminaires The LED package(s) / LED module(s) / LED array(s), including those incorporated into LED light engines or GU24 based integrated LED lamps, shall meet the following L70 lumen maintenance life values (refer to Lumen Maintenance Requirements in the next section):

• 25,000 hours for residential grade indoor luminaires

• 35,000 hours for residential grade outdoor luminaires

• 35,000 hours for commercial grade luminaires

Lumen maintenance life projection claims in excess of the above requirements shall be substantiated with a TM‑21 lumen maintenance life projection report.

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4

Characteristic Requirements

Lumen maintenance requirements:

directional and non-directional luminaires

The LED package(s) / module(s) / array(s), including those incorporated into LED light engines or GU24 based integrated LED lamps, shall meet the following

• L70(6k) rated lumen maintenance life values, in situ:

• L70(6k) ≥ 25,000 hours for residential indoor

• L70(6k) ≥ 35,000 hours for residential outdoor, or commercial

Compliance with the above shall be documented with a TM‑21 lumen maintenance life projection report as detailed in TM‑21, section 7. The report shall be generated using data from the LM‑80 test report for the employed LED package/module/array model (“device”), the forward drive current applied to each device, and the in situ TMP_LeD temperature of the hottest LED in the luminaire. In addition to LM‑80 reporting requirements, the following information shall be reported:

• sampling method and sample size (per LM‑80 section 4.3)

• test results for each T_S and drive current combination

• description of device including model number and whether device is an LED package, module or array (see Definitions)

• ANSI target, and calculated CCT value(s) for each device in sample set

• Δ u’v’ chromaticity shift value on the CIE 1976 diagram for each device in sample set

• a detailed rationale, with supporting data, for application of results to other devices (e.g. LED packages with other CCTs) Access to the TMP_LeD for the hottest LED may be accomplished via a minimally sized hole in the luminaire housing, tightly resealed with a suitable sealant if created for purposes of testing.

All thermocouple attachments and intrusions to luminaire housing shall be photographed.

CCT requirements: all indoor

luminaires The luminaire (directional luminaires), or replaceable LED light engine or GU24 based integrated LED lamp (non‑directional luminaires) shall have one of the following nominal CCTs:

• 2700 Kelvin

• 3000 Kelvin

• 3500 Kelvin

• 4000 Kelvin

• 5000 Kelvin (commercial only)

The luminaire, LED light engine or GU24 based integrated LED lamp shall also fall within the corresponding 7‑step chromaticity quadrangles as defined in ANSI/NEMA/ANSLG C78.377‑2008.

Color rendering requirements: all

indoor luminaires The luminaire (directional luminaires), or replaceable LED light engine or GU24 based integrated LED lamp (non‑directional luminaires) shall meet or exceed Ra ≥ 80.

Color angular uniformity

requirements: directional solid state indoor luminaires

Throughout the zonal lumen density angles detailed above, and five degrees beyond, the variation of chromaticity shall be within 0.004 from the weighted average point on the CIE 1976 (u’,v’) diagram.

Color maintenance requirements:

solid state indoor luminaires only The change of chromaticity over the first 6,000 hours of luminaire operation shall be within 0.007 on the CIE 1976 (u’,v’) diagram, as demonstrated by either:

• the IES LM‑80 test report for the employed LED package/array/module model, or

• as demonstrated by a comparison of luminaire chromaticity data in LM‑79 reports at zero and 6,000 hours, or

• as demonstrated by a comparison of LED light engine or GU24 based integrated LED lamp chromaticity data in LM‑82 reports at zero and 6,000 hours.

Source start time requirement:

Light source shall remain continuously illuminated within one second of application of electrical power.

Power factor requirements:

Total luminaire input power less than or equal to 5 watts: PF ≥ 0.5 Total luminaire input power greater than 5 watts:

Residential: PF ≥ 0.7 Commercial: PF ≥ 0.9 Transient protection requirements:

all luminaires Ballast or driver shall comply with ANSI/IEEE C62.41.1‑2002 and ANSI/IEEE C62.41.2‑2002, Class A operation. The line transient shall consist of seven strikes of a 100 kHz ring wave, 2.5 kV level, for both common mode and differential mode.

Operating frequency requirements:

Frequency ≥ 120 Hz

Note: This performance characteristic addresses problems with visible flicker due to low frequency operation and applies to steady‑

state as well as dimmed operation. Dimming operation shall meet the requirement at all light output levels.

Noise requirements: directional and

non-directional luminaires All ballasts & drivers used within the luminaire shall have a Class A sound rating.

Ballasts and drivers are recommended to be installed in the luminaire in such a way that in operation, the luminaire will not emit sound exceeding a measured level of 24 BA.

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2. DEfInE DEsIGn GoaLs

Based on the requirements given above, we chose the design goals for this project, shown in Table 5, to demonstrate the performance available from the XLamp MT‑G2 LED.

Table 5: Design goals

Characteristic unit Minimum Goal Target Goal

Light output lm 1200 > 1200

Luminaire efficacy lm/W 70 > 70

Lifetime hours 35,000 50,000

CCT K 3000 3000

CrI 100-point scale 80 > 80

Power W 18 < 18

Power factor 0.9 > 0.9

3. ESTImATE EffIcIENcIES Of ThE OpTIcAL, ThERmAL & ELEcTRIcAL SYSTEmS

We used Cree’s Product Characterization Tool (PCT) tool, shown in Figure 1, to determine the drive current for the design.

For the 1200‑lumen target, we estimated 90% optical efficiency and 87% driver efficiency. We also estimated a solder point temperature (T

_SP

) of 70 °C.

figure 1: pCT view of the number of LEDs used and driving current

The PCT shows that, at 450 mA, one MT‑G2 LED provides sufficient light output to meet the design goal.

Thermal Requirements

We used a commercially available downlight kit consisting of a heat sink, outer trim/housing, reflector and cover glass, shown in Figure 2. The heat sink is made of black anodized aluminum.

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LED System Comparison Report

System: 1,200 90% 87%

Model Model Model

Flux M0 [700] Tsp (ºC) 70 Flux Tj (ºC) 25 Flux Tj (ºC) 25

Price $ - Price $ - Price $ -

SYS # LED SYS lm tot SYS W SYS lm/W

0.350

2 2173.94 28.243 77 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

0.400

2 2396.26 32.543 73.6 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

0.450

1 1298.56 18.426 70.5 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

0.500

1 1388.72 20.577 67.5 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

0.550

1 1468.8 22.715 64.7 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

0.600

1 1539.37 24.833 62 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

0.650

1 1599.87 26.918 59.4 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

0.700

1 1651.28 28.965 57 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

0.750

#N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

0.800

#N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

0.850

#N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

0.900

#N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

0.950

#N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

1.000

#N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

1.050

#N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

1.100

#N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

1.150

#N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

1.200

#N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A

Target Lumens : Optical Efficiency: Electrical Efficiency:

Current (A)

LED 1 LED 2 LED 3

Cree XLamp MT-G: 36V {EZW} (none) (none)

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6 figure 2: mT-G2 downlight kit - Left: outer trim/housing, center: top and bottom views of reflector, right: heat sink

We performed thermal simulations to verify this thermal design is sufficient. Figure 3 shows the thermal simulation results for the design.

The simulated T

_SP

is 66 °C.

figure 3: Thermal simulation of MT-G2 downlight

Driver

The driver for this 3‑inch downlight can be located above the ceiling, apart from the downlight, and the size of the driver is not a factor in the design. We used a commercially available universal input voltage constant‑current driver.

4. CaLCuLaTE ThE nuMbER of LEDs

The purpose of this reference design is to show the lighting utility and excellent performance available from a single XLamp MT‑G2 LED.

The MT‑G2 LED is a multi‑chip LED package that can offer the required lumens with new levels of LED‑to‑LED color consistency and efficiency. The new MT‑G2 LED is 25% brighter than the original MT‑G, which can enable superior LED lighting designs even more quickly.

We selected a Warm White LED for this reference design, shown highlighted in yellow in Table 6. By choosing an LED from nearly the

highest flux bin, we ensured that the design takes full advantage of the LED’s capabilities.

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Table 6: MT-G2 LED order codes

Color CCT

Range

base order Codes min. Luminous flux (lm)

@ 1100 mA 2-step order Code 4-step order Code

Group flux (lm)

@ 85 °c flux (lm) @

25 °c

chromaticity

Region chromaticity

Region

Standard EasyWhiteCrI

3500 K

K0 650 748

35H

MTGBEZ‑00‑0000‑0B00K035H

35F

MTGBeZ-00-0000-0B00K035F

M0 700 805 MTGBEZ‑00‑0000‑0B00M035H MTGBeZ-00-0000-0B00M035F

N0 750 863 MTGBEZ‑00‑0000‑0B00N035H MTGBEZ‑00‑0000‑0B00N035F

3000 K

J0 600 690

30H

MTGBEZ‑00‑0000‑0B00J030H

30F

MTGBeZ-00-0000-0B00J030F

K0 650 748 MTGBEZ‑00‑0000‑0B00K030H MTGBeZ-00-0000-0B00K030F

M0 700 805 MTGBEZ‑00‑0000‑0B00M030H MTGBeZ-00-0000-0B00M030F

2700 K

H0 560 644

27H

MTGBEZ‑00‑0000‑0B00H027H

27F

MTGBEZ‑00‑0000‑0B00H027F

J0 600 690 MTGBEZ‑00‑0000‑0B00J027H MTGBeZ-00-0000-0B00J027F

K0 650 748 MTGBEZ‑00‑0000‑0B00K027H MTGBeZ-00-0000-0B00K027F

5. ConsIDER aLL DEsIGn possIbILITIEs

This reference design aims to show that a single MT‑G2 LED enables a downlight offering superior performance. This is only one of many ways to design an LED‑based downlight.

This design presents a number of desirable performance‑related benefits that are results of the XLamp MT‑G2 LED package. Because the MT‑G2 LED uses EasyWhite Technology, LED‑to‑LED color consistency can be held to within two or four McAdam ellipses for any given CCT, depending on the order code. The MT‑G2 LED is binned at 85 °C, so the CCT will be as faithful as possible to the system operating environment. These component features allow for new levels of specification accuracy.

However, the primary purpose of this reference design is to show how simple and straightforward it is to design with Cree’s XLamp MT‑G2 LED. This application note is not intended to show the only way to do this, but instead demonstrate the ease of implementation with this set of engineering constraints. Certainly numerous other successful solutions are possible.

The performance range of the XLamp MT‑G2 LED enables a wide variety of luminaires that all use a single LED. CCTs from 2700 K to 5000 K and lumen output levels up to 1987 lm in cool white and 1735 lm in warm white

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are available, providing the flexibility to offer a variety of luminaires that use a single LED light source and reflector.

6. CoMpLETE ThE fInaL sTEps: IMpLEMEnTaTIon anD anaLysIs

Using the methodology described above, we determined a suitable combination of an LED, components and drive conditions. This section

describes how Cree assembled the downlight and shows the results of the design.

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8 2. Following the recommendations in the MT Family Soldering and Handling document, we reflow soldered the MT‑G2 LED to the metal core printed circuit board (MCPCB).

3. We secured the MCPCB to the heat sink with a small amount of thermally conductive epoxy, making sure to center the LED on the heat sink.

4. After the thermal epoxy cured, we fed the driver output wires through the heat sink and soldered them to the LED.

5. We tested the connection by applying power and verified the LED lit up.

6. We covered the MCPCB with a piece of reflective paper that had a square opening the size of the MT‑G2 in its center.

7. The heat sink has threads to accept the housing and we screwed the housing to the heat sink.

8. We positioned the reflector over the LED, installed the cover glass, then screwed the front trim ring to the housing to secure the reflector and the cover glass.

9. We performed final testing.

Results

Thermal Results

Cree verified the board temperature with a thermocouple to confirm that the thermal dissipation performance of the heat sink aligns with our simulations. The measured solder point temperature was 64 °C.

Based on the measured solder point temperature, the T

_J

can be calculated as follows.

T

_J

= T

_SP

+ (LED power * LED thermal resistance) T

_J

= 64 °C + (17.5 W * 1.5 °C/W)

T

_J

= 90 °C

This thermal performance is in line with the thermal simulation.

Estimated LED Lifetime

Based on thousands of hours of long‑term testing of the MT‑G LED at higher temperatures than the measured 64 °C T

_SP

of the MT-G2 downlight, Cree expects an L70 lifetime significantly longer than 50,000 hours. The MR16 lamps commonly used in 3‑inch halogen downlights typically have lifetimes ranging from 1200 to 4000 hours, so the much longer lifetime of the MT‑G2 downlight greatly decreases the costs associated with replacing lamps.

Optical and Electrical Results

We tested the downlight in a 1.5‑meter sphere after a 60‑minute stabilization time to obtain the results in Table 7.

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As the table shows, the downlight meets the target goals for the design and also meets the ENERGY STAR efficacy, power factor, CCT and CRI requirements.

3 Testing was performed at the Cree’s Shenzhen Technology Center. An IES file for the downlight is available.

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Table 7: mT-G2 downlight steady-state results

Characteristic unit Downlight

Luminous flux lm 1300

Luminaire efficacy lm/W 75

Beam angle ° 46

CCT K 3086

CrI 100-point scale 80

Power W 17.5

Power factor 0.9

We also tested the intensity distribution of the downlight. Figure 4 shows an even intensity distribution with a 46° beam angle.

figure 4: Angular luminous intensity distribution of mT-G2 downlight

Table 8 shows the center beam illuminance of the MT‑G2 downlight at various distances from the light source.

Table 8: mT-G2 downlight illuminance – 46° beam angle

height Illuminance

Diameter

Eavg Emax Eavg Emax

1.0 m 3.3 ft 98.8 fc 161.7 fc 1,064.0 lx 17,401.0 lx 86.4 cm 2.8 ft

2.0 m 6.6 ft 24.7 fc 40.4 fc 266.0 lx 435.1 lx 170.8 cm 5.6 ft

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10 10

10 ConCLusIon

This reference design illustrates the ease of developing a 3‑inch downlight based on the Cree XLamp MT‑G2 LED. The downlight components are all commercially available, showing that a very capable luminaire can be designed without the time and expense of developing custom parts. Simplicity of use and lighting‑class performance make the Cree XLamp MT‑G2 LED an attractive design option for an LED‑based 3‑inch downlight.

bILL of MaTERIaLs

Table 9: bill of materials for MT-G2 3-inch downlight

Component order Code/Model number company Web Link

Driver ERP030W‑0420‑38 Energy Recovery Products, Inc. www.erecoveryinc.com

Heat sink, housing, cover glass,

reflector kit CLF0020-3 Xing Yi Lighting www.xingyilight.com/main.asp

LeD MTGBeZ-00-0000-0B00M030F Cree, Inc. MT-G2 product page

Thermal epoxy ASTA‑7G Arctic Silver, Inc. www.arcticsilver.com/arctic_silver_thermal_

adhesive.htm

Reliance on any of the information provided in this Application Note is at the user’s sole risk. Cree and its affiliates make no warranties or representations about, nor assume any liability with respect to, the information in this document or any LED‑based lamp or luminaire made in accordance with this reference design, including without limitation that the lamps or luminaires will not infringe the intellectual property rights of Cree or a third party. Luminaire manufacturers who base product designs in whole or part on any Cree Application Note or Reference Design are solely responsible for the compliance of their products with all applicable laws and industry requirements.

Cree XLamp MT-G2 LED 3-Inch Downlight Reference Design

ApplicAtion note 12 6 r ev 0 C